Wheat
Einkorn wheat (Triticum monococcum), one of the earliest domesticated crops. Source: Kurt Stueber
Wheat is any of a number of species of the genus Triticum within the grass family of Poaceae.
The wheat
harvest in Palouse, Idaho, USA. Source: USDA
Wheat is an important grain food crop supplying the second highest caloric intake for humans, closely behind rice. Wheat is used to
produce flour for bread, pasta, couscous and other foods.
However, wheat generally consumes large amounts of nitrate and other fertilizers, so that the outcome of widespread wheat farming is
often associated with extensive water pollution impacts, expecially related to nitrate laden runoff.
Wheat is one of the earliest cultivated crops, and has a clear association with the emergence of sedentaryagriculture around twelve
millennia ago.
Products Made From Wheat: 1. Crossaint; 2. Wheat Flour; 3. Noodles;
4. Wheat Dalia; 5. Sewai; 6. Refined Wheat Flour; 7. Common Brown Bread;
8. Semolina; 9. Pasta; 10. Cookie; and 11. Flat Bread
(Source: Saikat Basu, own work)
Wheat is one of the most adaptable of crops, grown from the equator to near the Arctic, and from sea level to the Tibetan Plateau. Recent
research demonstrates that production of the world wheat crop is likely to increase if atmospheric carbon dioxide levels rise.
Dry and Matured Wheat Seed (Source: Saikat Basu)To
feed the burgeoning worldwide human population explosion, intensification of wheat
farming has brought the by-product of increased crop diseases; such practices as intensive irrigation, lack of crop rotation and
dependence on monocultures have promoted the propagation of many fungal pathogenic infections that reduce the yields of wheat and
other cereal crops, and in some cases can lead to human disease via mycotoxin production.
History of cultivation
Domestication and cultivation of wheat
was
one of
the earliest farming
activities of prehistoric man, at the
outset of sedentary agriculture.
A number of sites in the Levant are
associated with early wheat cultivation,
a site at Iraq ed-Dubb (Cave of the
Bear), in present day Jordanis arguably
the oldest radiocarbon dated location at
9600 BC.
Other archaeological records from:
a.
The Abu Hureyra site in the valley of
the Euphrates in Syria
b.
The Nevalı Çori site; and (in southern
Turkey)
c.
From
Cayonu
in
the
Karacadag
Archaeological site of Volubilis with extant Roman ruins. @ C.Michael Hogan
Moutains of Turkey
At each site wheat cultivation is dated to the eight and ninth millennia BC.
Sites showing evidence of early wheat cultivation in the levant. Base map source: DEMIS
Even in North Africa, where the present day climate is arid, there is evidence of Neolithic farming of emmer wheat; for example at the
Volubilis archaeological site in Morocco, DNA analysis shows that the climate was mild and wet enough to support emmer production
thousands of years ago. The site was eventually developed to be the regional capital of the Phoenicians and Romans as a western outpost
for each of these conquering early colonial powers.
Principal species
There are several key species of wheat, chief among them being:

Bread Wheat (Triticum aestivum), anallohexaploid species most
commonly used in production of bread

Einkorn Wheat (Triticum monococcum), a [diploid] species with
2n=14

Wild Emmer (T. dicoccoides), a[tetraploid] hybrid formed by T.
urartuand an extinct wild grass of genusAegilops

Emmer Wheat (T. dicoccum), a tetraploid species derived from
wild emmer

Durum Wheat (T. durum), a tetraploid species derived from wild
emmer
Scientific Classification
Kingdom:
Plantae
(Plants)
Phylum:
Viridaeplantae
(Green
Plants)
Streptophyta
(Land
Plants)
-Tracheophyta
(Vascular
Plants)
--Spermatophytina
(Seed
Plants)
---Angiospermae
(Flowering
Plants)
Class:
Magnoliopsida
(Dicotyledons)
-Lilianae
(Monocotyledons)
Order:
Poales
(Grasses)
Family:
Poaceae
(Grasses)
Genus:
Triticum (Wheat)
Species: Many
Simplified Life Cycle of Wheat (Source: Saikat Basu, own work)
Evolution of Hexaploid Wheat (Source: Saikat Basu, own work)
Fertilizer requirements
Use of nitrate fertilizers for wheat production have been common in Western nations since the mid 1800s. In China, widespread use of
nitrates for wheat crops began in the 1950s subsequent to widespread famines. The concomitant outcome of massive nitrate usage is
broad water pollution impacts from nitrate and other chemical fertilizer usage, driven by surface runoff. In India, for example, wheat and
rice farming account for the vast majority of nitrate usage, even though other cereal grains constitute the majority of acreage planted to
cereal crops.
Water requirements
Desertification and aquifer overdrafting in evidence, North China Plain. @ C.Michael HoganApproximately
one cubic meter of water is required to
produce one kilogram of wheat. This value is about one half of the water needed to produce the same quantity of rice and one fifteenth
that to produce one kilogram of beef. Nevertheless, world demand for water to irrigate wheat crops is extraordinarily high, owing to the
massive amount of land planted to wheat.
Particular areas where overdrafting of groundwater have created ecological and agricultural disasters are the North China Plain and the
Great Plains of the USA overlying the Ogallala aquifer. In both cases the aquifer has been mined at an unsustainable level over a period
of decades, such that the peak agricultural yield was reached some time ago. In the case of the Ogallala aquifer, overmining of water has
been occurring since the 1940s, when cheap electrical power provided by misguided federal stimulus programs led to unsustainable
water extraction. In the case of the North China Plain, wheat production peaked in the 1990s as the depth to groundwater started to
become prohibitive in costs for some farms.
Worldwide production
Over the past fifty years (1961-2011) world wide wheat production tripled from 222 million tonnes to 704 million tonnes as shown in the
figure below using data from the Food and Agriculture Organization of the United Nations (FAO). During the same period the world's
population doubled (2.2-fold) from 3.1 billion to 6.9 billion (mid-year populations estismates from the UN)
Source: FAOSTAT, United Nations. 2012.
The dramatic increase in wheat production was not driven by a increase in land being farmed for wheat, which increased just 8% from
204 million hectares (2.04 million km2 or 788,000 miles2) to 220 million hectares (2.20 million km2 or.851,000 miles2).
Source: FAOSTAT, United Nations. 2012.
The increase in wheat production is primarily related to a nearly three-fold increase in yield, from an average of just 11,000 hectograms
(1.1 tonnes) of wheat per hectare on average to to nearly 32,000 hectograms (3.2 tonnes) per hectare (see figure below).
Source: FAOSTAT, United Nations. 2012.
The increase in yield has been due to a number of factors including:





New varieties/cultivars of wheat;
More irrigation and more effective methods of irrigation;
Wider use of pesticides and more effective pesticides;
Wider use of fertilizer and more effective fertilizers; and,
Improvements in argricultural practices and mechanization
Top Wheat Producing Nations
The top wheat producing nations of the world 2011 are as follows:
Nation
Wheat
(tonnes)
1.
China
117,410,300
2.
India
86,874,000
3.
Russia
56,240,000
4.
USA
54,413,300
5.
France
38,037,000
6.
Australia
27,410,100
7.
Canada
25,261,400
Production
8.
Pakistan
25,213,800
9.
Germany
22,800,000
10.
Ukraine
22,323,600
11.
Turkey
21,800,000
Source: United Nations. 2012. Searchable online statistical database from Food and Agriculture Division of the United Nations.
FAOSTAT
These eleven nations produced a total of 498 million tonnes or nearly 71% of worldwide production.
Changes in National Wheat Production over the Past Fiifty Years
In 1961, the USSR was the world largest produced followed by the USA, China, India, and France. In those fifty years, the most
dramatic increases in wheat production have occurred in China (8.2 times 1961 harvest), India (7.9 times), and, Pakistan (6.6 times).
Source: United Nations. 2012. Searchable online statistical database from Food and Agriculture Division of the United Nations.
FAOSTAT
Top Wheat Exporting Nations
However, the major wheat exporting countries are somewhat different than those of total production. In 2010, the country with the
highest export total was the USA, with 35.5 million tons, with deliveries largely to Nigeria, Mexico, Japan and Philippines; in a distant
second place was France with 19.2 million tons, with principal markets in North Africa. Close to France was the Canadian total export,
with 17.5 million tons, delivering chiefly to markets in China, Iran and Japan. Australia was the fourth largest wheat exporter with 13.5
million tons, mainly serving demand in China and Indonesia.
Source: Saikat Basu, own work
Comparison of Wheat and Other Major Food Crops
The following table summaries worldwide production, harvested area, and average yield for eleven major food crops in 2011 as reported
by the Food and Agriculture Organization of the United Nations.
Crop
Production
(tonnes)
Area
(Hectares)
Yield
(Hectograms/Hectare)
Sugar Cane
1,794,359,190
25,436,924
705,415
Maize
883,460,240
170,398,070
51,847
Rice
722,760,295
164,124,977
44,037
Wheat
704,080,283
220,385,285
31,948
Potatoes
374,382,274
19,248,586
194,499
Soybeans
260,915,871
102,993,246
25,333
Casava
252,203,769
19,644,071
128,387
Oil Palm Fruit
233,810,539
16,265,248
143,749
Tomatoes
159,023,383
4,734,356
335,892
Barley
134,279,415
48,603,576
27,627
Bananas
106,541,709
5,157,466
206,578
Source: United Nations. 2012. Searchable online statistical database from Food and Agriculture Division of the United Nations.
FAOSTAT
Diseases in wheat
Wheat leaf rust. Source: James Kolmer
Considerable research has been conducted in wheat diseases, owing to the fundamental importance of wheat as a human food staple.
Some of the chief diseases that affect wheat are: wheat leaf rust, Fusarium crown rot, powdery mildew, ergot, foliar blight and root rot.
Wheat leaf rust is typified by infestation by the windblown fungal pathogen Puccinia triticina, a diseaseorganism that can cause
significant damage to wheat and other grain crops; control can be effected by the fungicide class of triazoles, but more promising
techniques are being developed to use cultivars produced from DNAanalysis of disease resistant wheat strains.
Fusarium crown rot is induced by the fungal pathogen Fusarium pseudograminearum, a disease agent transmitted in the atmosphere or
via animal dispersal. As the name implies, this disease primarily infects the crown of the plant, but not only is plant growth and
development hindered, the pathogen generates a trichothecene mycotoxin that is harmful to animal or human consumers of infected
wheat. This pathogen is more limited in host than others, and infects only barley and wheat.
Powdery Mildew on Wheat Leaf (Source: Saikat Basu, own work)Powdery
mildew in wheat is caused by the fungal pathogenBlumeria graminis,
which particulary thrives in cool humid areas such as much of the eastern USA. Crop yields can be significantly reduced, with control
effected through chemical treatment or genetic resistance. The pathogen B. graminis overwinters in most fields and thus is difficult to
eradicate by ploughing or crop rotation techniques.
Micrograph of Powdery Mildew Fungal Mycelium
and Conidispores on Wheat Leaf (Source: Saikat Basu, own work)
Micrograph of Powdery Mildew Infecting Mycelia on Wheat
(Source: Saikat Basu, own work)
Micrograph of Pure Culture of Powdery Mildew
on PDA Culture Plate (Source: Saikat Basu, own work)
Relationship to atmospheric CO2 Both foliar blight and root rot can be caused by infection by the pathogen Bipolaris
sorokiniana. Besides attacking important crops such as wheat and barley, this organism can infect a wide variety of native grasses ahd
forbs, and operates on almost a worldwide basis. Control of this pathogen may be effected by crop rotation, seed quality control and
ploughing of fields in a pattern of precise timing.
Research in growth response of wheat to variations in atmospheric carbon dioxide demonstrate a small effect on wheat plant
development to elevated CO2 levels. The rate of development of leaf primordia was observed to accelerate according to reports in Carver
(2009); thus, increasing atmospheric carbon dioxide concentrations are expected to result in higher production levels of wheat, or a
reduced growing season necessary to bring the wheat crop to harvest.
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Source:
http://www.eoearth.org/view/article/51cbf3547896bb431f6ac8f3/?topic=51cbfc78f702fc2ba8129ea2